Understanding the conditions of dissolved organic matter (DOM) release from thawing peat in the Arctic regions and identifying the pathways of processing DOM by soil and aquatic heterotrophic bacteria are critical in the context of rapid climate change. Until now, experimental approaches did not allow quantitative predictions of temperature and biota effects on carbon release from peat in permafrost-affected aquatic environments. In this study, we incubated frozen peat and its aqueous leachate at various temperatures (4, 25 or Iodobacter 45 °C), with and without culturable heterotrophic bacteria sp., extracted from thermokarst lakes, to quantify the release and the removal rate of organic carbon (OC) with time. The metabolic diversity of the native microbial community associated with the substrates involved in OC processing was also characterized. Transmission electron microscopy revealed that, after degradation, the associated bacteria are mostly located in the inner parts of plant cells, and that the degradation of organic matter around bacteria is more pronounced at 4 and 25 °C compared to 45 °C. The metabolic diversity of heterotrophic bacteria was equally high at 4 and 25 °C, but lower at 45 °C. Regardless of the microbial consortium (native community alone or with added culturable heterotrophs), both the OC release from peat and the OC removal from peat leachate by bacteria were similar at 4 and 25 °C. Very low apparent activation energies of DOM biodegradation between 4 and 25 °C - 1 (-4.23 ± 12.3 kJ mol ) suggest that the short-period of surface water warming in summer would have an insignificant effect on DOM microbial processing. Such duration (1 - 3 weeks) is comparable with the water residence time in peat depressions and permafrost subsidences, where peat degradation and DOM microbial processing occur. This questions the current paradigm of a drastic effect of temperature rise on organic carbon release from frozen peatlands, and should be considered for modelling short-term climate impacts in these regions.

Payne, p Payne, p R.C., Brownlee, D., Kasting, J.F., 2020. Oxidized micrometeorites suggest either high CO or low N 2 2 during the Neoarchean. Proceedings of the National Academy of Sciences 117, 1360.

http://www.pnas.org/content/117/3/1360.abstract Significance: Paleosols (ancient soils) have been used to estimate CO concentrations during the Archean Eon, 2 4.0 to 2.5 Ga. However, different paleosol studies disagree with each other and with climate model estimates for ancient CO levels. Oxidized iron micrometeorites dated at 2.7 Ga represent a new CO proxy with which to 2 2 compare. These meteorites suggest that CO constituted 25 to 50% of the atmosphere at that time. This is easiest 2 to explain if the N partial pressure was lower than today so that the atmospheric greenhouse effect was modest 2 and the climate was cool, consistent with evidence for contemporaneous glaciation. et al. Nature Abstract: Tomkins et al. [A. G. Tomkins , 533, 235 - 238 (2016)] suggested that iron oxides contained in 2.7-Ga iron micrometeorites can be used to determine the concentration of O in the Archean upper 2 atmosphere. Specifically, they argued that the presence of magnetite in these objects implies that O must have 2 ∼ been near present-day levels ( 21%) within the altitude range where the micrometeorites were melted during entry. Here, we reevaluate their data using a 1D photochemical model. We find that atomic oxygen, O, is the most abundant strong oxidant in the upper atmosphere, rather than O . But data from shock tube experiments 2 suggest that CO itself may also serve as the oxidant, in which case micrometeorite oxidation really constrains 2 the CO /N ratio, not the total oxidant abundance. For an atmosphere containing 0.8 bar of N , like today, the 2 2 2 ∼ ∼ lower limit on the CO mixing ratio is 0.23. This would produce a mean surface temperature of 300 K at 2.7 2 p Ga, which may be too high, given evidence for glaciation at roughly this time. If N was half the present value, 2 and warming by other greenhouse gases like methane was not a major factor, the mean surface temperature ∼ would drop to 291 K, consistent with glaciation. This suggests that surface pressure in the Neoarchean may need to have been lower - closer to 0.6 bar - for CO to have oxidized the micrometeorites. Ultimately, iron 2 micrometeorites may be an indicator for ancient atmospheric CO and surface pressure; and could help resolve 2 discrepancies between climate models and existing CO proxies such as paleosols. 2

Peng, C., Tang, Y., Yang, H., He, Y., Liu, Y., Liu, D., Qian, Y., Lu, L., 2020. Time- and compound-dependent microbial community compositions and oil hydrocarbon degrading activities in seawater near the Chinese Zhoushan Archipelago. Marine Pollution Bulletin 152, 110907.

http://www.sciencedirect.com/science/article/pii/S0025326X20300254